Drag bushing for a centrifuge



NOV. 29, 1966 PROUDLOVE DRAG BUSHING FOR A CENTRIFUGE Filed Dec. '7, 1964 Clearances Permir Free Rowurion Of Eiemenl' 50.

INVENTOR. JOSEPH PR UDLOVE ATTORNEY United States Patent 3,288,361 DRAG BUSHING FOR A CENTRIFUGE Joseph Proudiove, Meadowood, Newark, Del., assignor to Pennsalt Chemicals Corporation, Philadelphia, Pa., a corporation of Pennsylvania Filed Dec. 7, 1964, Ser. No. 416,343 2 Claims. (Cl. 23323) This invention relates to centrifuges. More specifically this invention relates to centrifuge drag bushings and provides for remarkable improvement in their wearing characteristics.

In the prior art it has been common to construct centrifuges in which the centrifuge bowl has a vertical axis and is suspended by supporting and driving means. Such a centrifuge is generally shown in US. Patent 1,232,104, which issued July 3, 1917, on an application filed by Philip T. Sharples. Safety means surround the lower end of the bowl to absorb some of the energy of the bowl as the bowl passes through critical speeds. This avoids excessive lateral excursions of the bowl. The safety means comprise what is generally referred to as a drag bushing.

In the past drag bushings have comprised springmounted annular bushing elements preferably of carbon composition. At critical speeds or at other times of instability the lower end of the centrifuge will bump against the bushing and will be limited in lateral movement by the annular bushing element. It should .be noted that another reason for provision of such safety means is that frequently the centrifuge is mounted on a moving frame, for instance, on a ship which may pitch and roll at sea. In such circumstances if the bowl is allowed to hang freely, it may engage the bowl casing as the ship moves. This could result in damage to the bowl, the casing, or both.

Past experience has been that the centrifuge drag bushing elements of the prior art, and particularly those in marine use, have lasted only for 30 to 90 days of continuous use before they have been so abraded by the lower end of the centrifuge bowl that they become inefficient. Typically the bushing element will wear so that its circular opening becomes egg-shaped. At this point the element must be replaced.

I have found that by altering the manner of operation of the drag bushing of centrifuges of the indicated type, the longevity of the annular bushing element may be increased to a remarkable and unexpected degree. It is, therefore, an object of the invention to provide a centrifuge drag bushing of remarkable wear characteristics.

Other objects of the invention will be apparent from a reading of the attached specification including drawings wherein:

FIGURE 1 is a fragmentary sectional view of the lower end of a centrifuge of the general type with which the invention is concerned and embodying the invention; and

FIGURE 2 is an exploded view showing the organization of a drag bushing embodying the invention.

Briefly, the invention in a centrifuge of the indicated type is the improvement in which the bushing element of the centrifuge drag bushing is mounted for free rotation.

Referring more specifically to the drawings, an apparatus embodying the invention is shown in FIGURE 1 and generally designated It comprises a casing 12 in which a centrifuge bowl 14 is mounted on a vertical axis. The lower end of the casing is provided with an opening 16 in which is mounted combined feed tube and drag bushing mount 18.

The lower end of the centrifuge bowl 14 carries a lower end cap 20 which presents a downwardly extending boss 22. Through the boss extends a central opening 24 for reception of feed mixture.

3,288,361 Patented Nov. 29, 1966 As shown, the combination feed tube and drag bushing mount 18 is provided with the feed passage 26 which presents an opening facing upwardly toward the bowl. A feed nozzle assembly 28 is secured over the opening and has a restricted outlet 30 which directs the feed upwardly into the bowl through the opening 24.

Surrounding the feed nozzle assembly 28 the combination feed tube and drag bushing mount presents upwardly directed faces to which are secured resilient elastomeric damping means 32. To the upper end of the damping means is secured the drag bushing housing 34.

Centrally the housing 34 presents an upwardly facing cup-shaped element 38 having a central opening in its lower end providing ample clearance for the feed nozzle assembly 28. A compression spring 40 sits on the annular bottom wall of the cup-shaped element 38 about the nozzle assembly 28 and supports a Washer 42 which carries the drag bushing parts shown in FIGURE 2.

More specifically the parts include the shell 44 preferably of steel and disposed in the upper end of the cupshaped element 38. Into the shell is tightly fitted a ferrule 46 which is preferably of brass. The ferrule is formed with a recess presenting an upwardly facing ledge 48. An annular drag bushing element 50, preferably of carbon composition, for instance a material known in the trade as Graphitar, is provided about its upper end with an outward annular flange 52.

In assembly the bushing element 50 is received within the opening of the ferrule 46 and the flange 52 sits on the ledge 48 of the ferrule. Clearance between the outer diameters of the bushing element 50 and the ferrule are such that the bushing element is free to rotate within the ferrule. Yet the dimensions of the bushing element are not so much smaller than the inner dimensions of the ferrule as to result in a sloppy rattling fit which would hinder the effectiveness of the drag bushing as a damping device.

The shell 44 is provided with a protective lip 54 to guard the drag bushing part against intrusion of dirt which could impair relative rotary motion between the bushing element and ferrule.

Referring again to FIGURE 1, a nut or annular cap 56 is secured about the mouth of the cup-shaped element 38 and holds the drag bushing downward against the upward urging of the spring 40.

By virtue of the structure disclosed, the bowl boss 22 upon engaging the bushing element 50 will cause the element to spin in the same rotary direction as the bowl. In comparable centrifuges of the prior art the bushing element has not rotated upon such engagement.

In centrifugal oil clarifying operations it has been found that the usual presence of oil in the casing is sufficient to lubricate the drag bushing of the invention. In other applications lubrication means may be used if desired or necessary.

In the form of drag bushing illustrated the damping means comprise the resilient mounts for the bushing housing. However, the damping means may take the form of springs radially disposed within the housing and biasing the ferrule into its proper central position. In the latter organization the bushing housing may be rigidly mounted in the centrifuge casing, for instance on the feed tube and drag bushing mount 18. In place of radial springs a rubber ring as disclosed for instance in US. Patent 3,061,181 may be used.

It is to be understood that the above particular description is by way of illustration and not of limitation, and that changes, omissions, additions, substitutions, and/ or other modifications may be made without departing from the spirit of the invention. Accordingly, it is intended that the patent shall cover, by suitable expression in the claims, the various features of patentable novelty that reside in the invention.

I claim:

1. In a centrifuge having a bowl disposed normally on a vertical axis and suspended by supporting and driving means, and a drag bushing assembly disposed at the lower end of the bowl and comprising an inner annular bushing element biased toward a position concentric with the axis and having its inner periphery circumposing and normally spaced outward from the lower end of the bowl, the improvement in which the bushing element is mounted for free rotation.

2. A centrifuge having a bowl disposed normally on a vertical axis and suspended from its upper end, a downward boss comprising the lower end of the bowl, a drag bushing mounted at the lower end of the bowl, the bushing including a cup-shaped housing, an annular shell disposed in the upper end of the cup-shaped housing, an annular ferrule disposed in the shell and presenting an upwardly facing shoulder, an annular drag bushing element disposed in the ferrule for free rotation therein and having an outward annular flange sitting on the shoulder of the ferrule, the bushing element surrounding the boss, the inner periphery of the bushing element being larger than and spaced from the boss, the shell having an inward lip extending over the flange on the bushing element to guard against intrusion of dirt between the ferrule and the bushing, an annular cap secured to the upper end of the cup-shaped housing and a spring resting on the bottom wall of the cup-shaped housing and urging the shell, ferrule and bushing element upward toward the annular cap, and damping means biasing the bushing element into concentric relation about the bowl axis.

References Cited by the Examiner UNITED STATES PATENTS 1,232,104 7/1917 Sharples 233-46 XR 1,401,196 12/1921 Sharples 233-2l 1,445,722 2/1923 Sharples 233-21 1,679,790 8/1928 Sharples 23321 1,750,154 3/1930 Bath 23347 M. CARY NELSON, Primary Examiner.

H. KLINKSIEK, Assistant Examiner. 

1. IN A CENTRIFUGE HAVING A BOWL DISPOSED NORMALLY ON A VERTICAL AXIS AND SUSPENDED BY SUPPORTING AND DRIVING MEANS, AND A DRAG BUSHING ASSEMBLY DISPOSED AT THE LOWER END OF THE BOWL AND COMPRISING AN INNER ANNULAR BUSHING ELEMENT BIASED TOWARD A POSITION CONCENTRIC WITH THE AXIS AND HAVING ITS INNER PERIPHERY CIRCUMPOSING AND NORMALLY SPACED OUTWARD FROM THE LOWER END OF THE BOWL, THE IMPROVEMENT IN WHICH THE BUSHING ELEMENT IS MOUNTED FOR FREE ROTATION. 